As is known, agricultural machinery of the towed type is provided with a member to be coupled to the towing means, which is typically a tractor.
This coupling member, commonly known as a drawbar, is essentially formed by one or a plurality of connecting arms rigidly secured to the frame of the agricultural machine.
At the end of the connecting arm opposite the frame of the agricultural machine, the coupling members are provided with a connection to the tractor, formed for instance by a hole which engages with a corresponding member secured to the tractor or a spherical joint.
Examples of these structures are disclosed in US Patent Specification U.S. Pat. No. 6,092,609.
It will be appreciated that the connecting arm has to have an intermediate member able to ensure that the vehicle towing the agricultural machine can be manoeuvred.
In the case of a seeder, the tractor must have sufficient mobility in seeding operations during end-of-field manoeuvres and in road traffic.
In known agricultural machinery, the presence of the coupling member therefore entails a high longitudinal bulk which is particularly disadvantageous when transporting and storing the machine.
This problem is partly resolved by some agricultural machinery, for instance that disclosed in US Patent Specification U.S. Pat. No. 6,068,062, in which the frame of the seeder devices may be folded towards the drawbar, thereby reducing their overall bulk.
This solution is nevertheless relatively complex from the point of view of its construction and entails high production costs.
It should in particular be noted that in order to be able readily to fold the frame, actuators of various types have to be provided in view of the weights to be moved.
A further example of drawbar is disclosed in EP 289 773, relating to a agricultural hitching device formed by a four-bar linkage. Such solution is directed to obtain as small a turning radius as possible and a low oblique pull or low lateral force on the hitching device and, furthermore, to carry out turning operations without an interruption of the drive.
Nevertheless, the hitching device discloses in EP 289 773 is particularly bulky and the presence of a four-bar linkage represents a serious drawback when the machine is stored or transported.